Positioning system for a nerve stimulator needle

ABSTRACT

A target nerve or nerve plexus registration point is located utilizing a nerve stimulator needle positioned in a bore of a carrier. The carrier is configured with an electrically nonconductive smooth curved surface at a distal end of the bore. The needle tip is fixed in an operative cutaneous electrode position and the smooth curved surface of the carrier is forced against and compresses the epidermis, corium and subcutaneous tissue and traverses cutaneous surfaces to locate a target nerve or nerve plexus without physical penetration by the needle tip. The needle is then inserted at the located point, with or without the needle path being guided by the bore. In another embodiment, a subcutaneous portion of carrier is introduced and is pivoted about its introduction point to locate the target nerve.

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 60/408,026, filed Sep. 4, 2002.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to regional anesthesia and more particularly to a system for positioning a nerve stimulator needle in conjunction with various procedures, such as, the administration of an anesthetic blockade, neuro monitoring, electromyography and therapeutic intervention.

[0004] 2. Antecedents of the Invention

[0005] The field of regional anesthesia relates to the practice of administering anesthesia to a specific body region during surgery, for the relief of postoperative pain, and for extended relief of trauma or chronic pain. Often, regional anesthesia has been found to be preferable to general anesthesia because of increased safety, the availability of postoperative pain control and decreased anesthetic costs.

[0006] Regional anesthesia delivery techniques strove to optimize administration of a local anesthetic in close proximity to a target or nerve plexus so as to establish a neural blockade. Successful administration of regional anesthesia was dependent upon the accurate placement of the anesthetic in relation to the target nerve or nerves.

[0007] Various techniques have been employed to assist in placement of an administration needle in close proximity to the target nerve, which was not externally visible. One of the traditional methods of needle placement involved eliciting paresthesia. Among the disadvantages of this technique was the lack of accurate patient responses amongst patients who were disoriented and/or sedated.

[0008] A prevalent technique employed the use of nerve stimulators electrically coupled to a nerve stimulator needle. Such method was premised upon the phenomenon that an electrical pulse is capable of stimulating a motor nerve fiber to contract an innervated muscle or cause paraesthesia, in the case of sensory nerve stimulation.

[0009] The nerve stimulator needle was placed within the tissue of the patient's body in the vicinity of the nerve to be blocked and then advanced until stimulation of the target nerve was achieved as determined by visually detecting muscle contractions or by eliciting a report that the patient felt the stimulus in response to the current flow through the stimulator needle.

[0010] The current supplied by the nerve stimulator was reduced as the nerve stimulator needle was further advanced, until stimulation of the target nerve was achieved using a reduced current level associated with a prescribed distance between the needle tip and the target nerve.

[0011] Thereafter, a portion of the anesthetic dose was administered through the needle to terminate the response to the nerve stimulation current. If the response was terminated by the initial administration, the needle was deemed to be properly positioned in proximity to the target nerve and the remaining dose of anesthetic was administered.

[0012] It should be understood, however, that the initial placement of the needle was dependent upon anatomic landmarks. Since anatomic landmarks varied from patient to patient, they constituted only an approximate starting zone or region to guide needle insertion. Successful administration was often dependent upon the skill and experience of the anesthesiologist. Multiple needle passes were required when the initial needle placement was not directly registered over the target nerve or nerve plexus or when the angle of introduction was anatomically incorrect.

[0013] Peripheral nerves have been stimulated with cutaneous electrodes at appropriate landmarks utilizing a coupling gel for monitoring the degree of neuromuscular blockade during general anesthesia when neuromuscular relaxing or paralyzing drugs were intravenously administered.

[0014] In U.S. Pat. No. 6,533,732, entitled: NERVE STIMULATOR NEEDLE GUIDANCE SYSTEM issued Mar. 18, 2003 to Applicant, there is disclosed a nerve stimulator needle guidance system having a cutaneous electrode with a conductive tip and a bore extending through the electrode. The electrode is coupled to a nerve stimulator to noninvasively locate a target nerve registration point while depressing the patient's dermal layers. Thereafter a nerve stimulator needle is introduced through the bore and into the patient at the located registration point. There is also disclosed, in Applicant's Application No. PCT/US01/32412, published Apr. 25, 2002, Publication No. 02/32289 82 a subcutaneous electrode guidance system for a nerve stimulator needle which utilized a smooth tipped electrode probe for locating the direction of a nerve or nerve plexus relative to a cutaneous introduction point.

SUMMARY OF THE INVENTION

[0015] The tip of a nerve stimulator needle electrode is physically restrained against penetration through the corium while serving as a cutaneous electrode for locating a nerve or nerve plexus registration point. The needle is positioned within a bore of an electrically shielded nonconductive carrier having a smooth, blunt, shield at one end and is locked into a position such that the needle tip does not project beyond the shield a distance sufficient to penetrate the epidermis and corium while the carrier is depressed against and laterally displaced along dermal layers.

[0016] A set screw may be employed to bear against the needle shaft or hub for fixing the needle tip. Alternatively, a spring-loaded latch may bear against an indexing groove in the needle shaft or hub for fixing the needle tip. In a further embodiment, a snap fit engagement between the carrier and the nerve stimulator needle may be provided for fixing the needle tip.

[0017] The target nerve cutaneous registration point is located by applying a suitable current through the needle while depressing the patient's dermal layers with the shield and traversing a cutaneous zone until a suitable neuromuscular response is elicited. Thereafter the bore may be utilized as a guide for advancing the needle or the carrier may be removed, i.e. separated from the needle, or positioned adjacent the proximal end of needle while the needle is advanced into the patient.

[0018] The needle shaft or hub may include a radial arm which is received in a vertical slot of the carrier for fixing the position of the needle tip and/or advancing the needle into the patient at the located registration point.

[0019] In a further embodiment, a subcutaneous guiding electrically shielded nonconductive carrier includes a smooth blunt end. The subcutaneous carrier is introduced through the skin utilizing a needle carried in a bore and projecting beyond the blunt end. The needle is then retracted so that the tip is flush or slightly recessed from the blunt end.

[0020] The blunt end is advanced to a desired depth beneath the skin fixed by a smooth lateral stop surface and the carrier is manipulated in a sweep pattern while the needle tip is maintained flush with or recessed from the contour of the blunt end. Nerve stimulation current is applied to the needle tip during manipulation to locate the direction of the target nerve relative to the introduction point. Axial pressure may be applied through the surface of the stop to compress the surrounding dermal layers during manipulation of the carrier.

[0021] After the direction of the target nerve is located, the position of the carrier is fixed and the nerve stimulator needle is advanced through the bore and beyond the blunt end, while applying a reduced level of current. When appropriate muscle contractions are elicited at low current levels, the nerve stimulator needle has been properly positioned for administration of anesthesia.

[0022] From the foregoing compendium, it will be appreciated that it is an aspect of the present invention to provide a positioning system for a nerve stimulator needle of the general character described which is not subject to the disadvantages of the antecedents of the invention.

[0023] It is a feature of the present invention to provide a positioning system for a nerve stimulator needle of the general character described, which simplifies the administration of neural blockade anesthesia.

[0024] Another aspect of the present invention is to provide a positioning system for a nerve stimulator needle of the general character described which utilizes a tip of a nerve stimulator needle to noninvasively locate a cutaneous entry point for the needle.

[0025] An additional feature of the present invention is to provide a positioning system for a nerve stimulator needle of the general character described with simplified electrical connection to a nerve stimulator current generator for both locating a cutaneous registration point of a target nerve and for advancement of a nerve stimulator needle toward the target nerve.

[0026] To provide a positioning system for a nerve stimulator needle of the general character described which is well suited for the introduction of a catheter for continuous regional anesthesia or analgesia is a further consideration of the present invention.

[0027] Another aspect of the present invention is to provide a cutaneous electrode which does not require the use of a coupling gel.

[0028] A still further feature of the present invention is to noninvasively employ a needle electrode on cutaneous surfaces in conjunction with a medical procedure.

[0029] An additional consideration of the present invention is to provide a positioning system for a nerve stimulator needle of the general character described which increases the efficiency of the administration of regional anesthesia.

[0030] To provide a positioning system for a nerve stimulator needle of the general character described which utilizes conventional nerve stimulators is yet a further aspect of the present invention.

[0031] Other aspects, features and considerations of the present invention in part will be obvious and in part will be pointed out hereinafter.

[0032] With these ends in view, the invention finds embodiment in certain combinations of elements, arrangements of parts and series of steps by which the aforesaid aspects, features and considerations and certain other aspects, features and considerations are attained, all with reference to the accompanying drawings and the scope of which will be more particularly pointed out and indicated in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In the accompanying drawings in which are shown some of the various exemplary embodiments of the invention:

[0034]FIG. 1 is a schematized illustration of a positioning system for a nerve stimulator needle constructed in accordance with and embodying the invention as may be typically employed to locate a target median nerve and illustrating a nerve stimulator needle positioned within the bore of a carrier, with the needle being coupled to a nerve stimulator,

[0035]FIG. 2 is a perspective view of the positioning system illustrating a cylindrical carrier having an axial bore and a smooth blunt shield at one end and with the needle fixedly positioned within the bore such that the needle tip is substantially flush with the contour of the shield,

[0036]FIG. 3 is an enlarged scale sectional view through the carrier and illustrating a set screw which bears against the needle shaft for maintaining the needle tip in position,

[0037]FIG. 4 is an enlarged scale sectional view through a modified carrier illustrating a spring biased pin which bears against the needle shaft to fix the position of the needle,

[0038]FIG. 5 is an enlarged scale sectional view through the carrier and illustrating a further embodiment wherein a spring biased latch engages a groove formed in the needle shaft to fix the position of the needle,

[0039]FIG. 6 is a perspective view of an alternate embodiment of the positioning system wherein the carrier is spherically shaped and includes a manipulating handle,

[0040]FIG. 7 is a perspective illustration a further alternate embodiment, wherein the carrier includes an enlarged bore extending from a proximal end and with a needle hub seated in the bore and with a radial arm projecting from the needle shaft.

[0041]FIG. 8 is a sectional view through the positioning system illustrated in FIG. 7 and illustrating the technique of employing the positioning system for locating a femoral nerve,

[0042]FIG. 9 is an enlarged scale front elevational view of an alternate embodiment of the positioning system illustrated in FIG. 7 wherein the radial arm is selectively seated in a notch for fixing the position of the needle tip,

[0043]FIG. 10 is a fragmentary large scale front elevational view similar to that of FIG. 9 illustrating a further embodiment wherein the radial arm is seated in a toothed notch for fixing the position of the needle tip,

[0044]FIG. 11 is a perspective illustration of the FIG. 9 embodiment configured for conventional needle insertion after a cutaneous registration point has been located, and

[0045]FIG. 12 is a sectional view through a further embodiment of the invention including a subcutaneous carrier having an enlarged grip which is employed for depressing dermal layers while manipulating the carrier to locate the direction of a target nerve.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] With reference now in detail to the drawings, wherein like numerals denote like components throughout the various figures, the reference numeral 10 denotes generally a positioning system for a nerve stimulator needle constructed in accordance with and embodying the invention.

[0047] The positioning system 10 includes a carrier 12, illustrated in FIG. 2 as having a cylindrical body with an axial bore 14 extending therethrough. The carrier is formed of a material which is not electrically conductive, e.g. a thermoplastic. The distal end of the carrier comprises a blunt, smooth, rounded, shield 16 which may be of hemispherical shape. A conventional nerve stimulator needle 18 includes a hub 20 at its proximal end from which extends a conventional Luer fitting 22. A needle shaft 24 extends axially from the hub 20 and an electrical lead 26 interconnects at least a tip 28 of the needle shaft with a conventional nerve stimulator 30 illustrated in FIG. 1.

[0048] In accordance with the invention, there is provided a locking mechanism for engaging the needle shaft to temporarily lock the needle shaft 24 in an operative cutaneous electrode position wherein the needle tip 28 is flush with, slightly recessed from, or does not project beyond the contour of the shield 16 a distance sufficient to invasively penetrate into dermal layers, when the shield 16 is depressed against the dermal layers and laterally moved to locate a target nerve while in electrical contact with the dermal layers as will be explained in detail hereinafter.

[0049] As illustrated in FIG. 3, a set screw 32 having an actuating arm 34 may be threadably seated in a transverse bore of the carrier and may be engaged to bear down against the needle shaft 24 to fix it in position.

[0050] With reference to FIG. 1, the nerve stimulator 30 includes known pulse generating and adjustable current control circuits, with an output terminal 36 connected to the electrical lead 26. There is additionally provided an output terminal coupled to a ground lead 38. The nerve stimulator 30 also includes conventional output current controls 40, 42.

[0051] As explained in detail in U.S. Pat. No. 6,533,732 and published application—PCT/US01/32412 both of which are both of which are incorporated herein by reference, for each of the various target nerves, optimal initial (cutaneous) or base level current flow values are provided.

[0052] Pursuant to the invention, the shield 16 of the carrier 12 is forced against, compresses and indents the patient's dermal layers, i.e. epidermis, corium and subcutaneous tissue, in an anatomic cutaneous zone consistent with the target nerve or nerve plexus. With the dermal layers and subcutaneous tissue indented, the needle tip is brought closer to the target nerve, thus facilitating transcutaneous stimulation to locate the nerve. The carrier then moves the needle tip across the cutaneous zone while pressure is maintained with current being transmitted through dermal layers and without the requirement for utilizing a coupling gel. A cutaneous registration point is located when it is determined that appropriate muscle contractions have been elicited with minimum current.

[0053] Thereafter the set screw 32 may be released and the needle shaft 24 is urged through the carrier bore 14 and into the patient, utilizing the carrier bore 14 as a guide and with reduced current flow from the current generator. Maintenance of the compressive force on the dermal layers and underlying tissue serves to fix the position of the target nerve while the needle is being advanced.

[0054] When nerve stimulation is achieved utilizing a reduced current level associated with the prescribed distance between the needle grip 28 and the target nerve, a portion of the anesthetic dose is administered from a syringe 44 through flexible tubing 46 which is connected to the Luer fitting 22. If the response terminates with the initial administration, the needle is deemed to be properly positioned for the procedure.

[0055] Upon completion of the procedure and removal of the needle shaft from the patient, it is preferable to withdraw the needle shaft into the bore 14 until the needle tip 28 is recessed within the bore to prevent inadvertent needle sticks. The used needle may be locked in such safety position utilizing the set screw 32 and thereafter the needle may be discarded in an appropriate manner.

[0056] It should also be appreciated that the positioning system of the present invention is readily adapted for determining a cutaneous registration point with the needle 18 thereafter inserted at the located point without utilizing the bore 14 as a guide. In such instance, after releasing the set screw 32, the carrier 12 is slid up the needle shaft to the proximal (hub) end and fixed in such position. The anesthesiologist is then free to insert the needle to locate the target nerve in a conventional manner.

[0057] In FIG. 4 there is disclosed an alternate embodiment of the positioning system wherein like reference numerals have been employed to denote like components, however, bearing the suffix “a”. In this embodiment, an alternate mechanism is employed for maintaining a tip 28 a of a needle shaft 24 a within a bore 14 a of a carrier 12 a in a position for noninvasive electrical contact with dermal layers as described with reference to the preceding embodiment.

[0058] A transverse radial bore of the carrier 12 a intersects the bore 14 a and carries a pin 50 a which bears against the needle shaft 24 a. A compression spring 52 a is carried within the transverse bore between the pin 50 a and an external plug 54 a.

[0059] In FIG. 5 a further embodiment of the invention is illustrated wherein like numerals are employed to denote like components of the prior embodiments, however, bearing the suffix “b”. In this embodiment, a transverse radial bore of a carrier 12 b includes a latch pin 50 b which is urged against a needle shaft 24 b by a spring 52 b, with the spring being carried in the transverse bore between the pin 50 b and a plug 54 b.

[0060] The pin 50 b engages a groove 56 b of the shaft 24 b for fixing a position of a needle tip 28 b in an operative cutaneous electrode position, i.e. slightly recessed from, flush with or which does not extend beyond the contour of a shield 16 b so as to penetrate, but is in electrical contact with the dermal layers. A further groove 58 b is provided in the needle shaft 24 b in order to secure the needle tip within a bore 14 b after the procedure has been completed, so as to avoid inadvertent needle sticks. An additional groove (not shown) may be provided to fix the carrier along the needle shaft 24 b at a position adjacent the needle hub, which would enable a practitioner to advance the needle into the patient at the located point in a conventional manner, i.e. without utilizing the bore 14 b as a guide.

[0061] In FIG. 6 there is illustrated a further embodiment of the invention wherein like numerals have been employed to denote like components, however bearing the suffix “c”. In this embodiment, a spherical carrier 12 c having a bore 14 c is employed. An integral manipulating handle 58 c projects from the surface of the carrier 12 c. The handle 58 c is employed to both exert pressure for compressing dermal layers and underlying tissue as well as for movement of the carrier 12 c along cutaneous surfaces.

[0062] In another embodiment of the positioning system illustrated in FIG. 7 and FIG. 8, like numerals have been employed to denote like components, however bearing the suffix “d”. In this embodiment, an elongated cylindrical carrier 12 d includes an enlarged proximal bore 62 d having a diameter sufficient to accommodate a hub 20 d as well as a Luer fitting 22 d of a needle 18 d. Adjacent the distal end of the carrier 12 d, a coaxial bore 14 d is provided for accommodating a needle shaft 24 d. Connected to the needle shaft 24 d through the hub 20 d is a nerve stimulator electrical lead 26 d and a length of tubing 46 d interconnects the Luer fitting 22 d with a syringe.

[0063] The tip of the needle 18 d is maintained in operative cutaneous electrode position by an annular integral rib 64 d, formed on the interior surface of the bore 62 d adjacent its proximal end. The rib 64 d is in snap fit engagement with an annular groove 66 d formed in the hub 20 d.

[0064] It should be noted that the carrier 12 d includes a longitudinal slot 68 d and a radial arm 70 d extends from the needle shaft 24 d through the slot. The arm 70 d may be manipulated axially to urge the needle 18 d into the patient at the located registration point. Indexing marks 72 d are optionally provided along the slot 68 d to gauge the depth of penetration. FIG. 8 illustrates the positioning system in use for locating a point in registration with a target femoral nerve 74 d.

[0065] In FIG. 9 there is shown a variation of the embodiment of FIG. 7 and FIG. 8 wherein one longitudinal edge of a slot 68 e includes spaced notches or indentations 76 e, with a radial arm 70 e projecting from a needle shaft being rotated from the slot 68 e and seated in a selected notch to fix the position of the needle shaft. The selected notch may be one for positioning the tip of the needle in operative cutaneous electrode position or for safely receiving the tip of the needle within the carrier after the needle is withdrawn from the patient. In FIG. 10, the arm 70 e is seated in a notch position wherein the major portion of a needle shaft 24 e is accessible for insertion into the patient at the located registration point without utilizing the needle receiving bore of the carrier 12 e as a guide.

[0066] In a still further modification is illustrated in FIG. 11, wherein a plurality of angular notches 76 f are provided along an edge of a slot 68 f and a portion of a radial arm 70 f is angularly configured for locking engagement with a desired notch to facilitate advancement of the needle shaft and retard retraction into the carrier.

[0067] With reference now to FIG. 12 wherein a further embodiment of the invention is illustrated, like numerals have been employed to denote like components of the prior embodiments, however bearing the suffix “g”.

[0068] A relatively small diameter generally cylindrical subcutaneous guiding carrier 80 g includes a smooth distal end 82 g and a large diameter concentric proximal gripping portion 84 g. The gripping portion 84 g is interconnected to the subcutaneous guiding carrier 80 g at a curved step 86 g which provides a depth of penetration stop as will be pointed out hereinafter. A bore 14 g, dimensioned to receive a needle shaft 24 g, extends concentrically through the subcutaneous guiding carrier 80 g and the grip 84 g.

[0069] The subcutaneous guiding carrier 80 g is introduced through the dermal layers at a penetration point utilizing a needle tip 28 g with the needle shaft 24 g being positioned to extend the tip 28 g beyond the smooth distal end 82 g. The needle shaft 24 g is then withdrawn into the bore 14 g until the needle tip 28 g is flush with or slightly recessed from the distal end 82 g.

[0070] After the subcutaneous guiding carrier 80 g reaches a desired depth of penetration which is fixed by the step 86 g, the guiding carrier 80 g is manipulated in a sweep pattern, while nerve stimulation current is applied. The smooth distal end 82 g of the subcutaneous carrier 80 g reduces the trauma which would otherwise result if an exposed needle tip were manipulated in the sweep pattern.

[0071] When the direction of a target nerve 88 g is determined through elicitation of a suitable neural response at reduced current levels, the position of guiding carrier 80 g is held fast. Thereafter the needle shaft 24 g is advanced through the bore 14 g, while applying a reduced level of current until the needle tip is properly positioned in proximity to the target nerve 88 g for the administration of anesthesia.

[0072] It should also be appreciated that the subcutaneous guiding carrier 80 g may be employed in a different medical procedure, such as imaging. In such instance, the guiding carrier 80 g may comprise an ultrasonic or other imaging probe. After the direction of the target nerve or other subcutaneous target zone is determined utilizing the nerve stimulator needle tip, the needle current supply is discontinued and the ultrasonic or imaging probe is activated.

[0073] Thus is will be seen that there is provided a positioning system for a nerve stimulator needle which achieves the various aspects, features and considerations of the present invention and which is well suited to meet the conditions of practical usage.

[0074] As various possible further embodiments might be made of the present invention and various changes might be made in the illustrative embodiments above set forth without departing from the spirit of the invention, it is to be understood that all matter herein described or shown in the accompanying drawings is to be interpreted as illustrative and not in a limited sense. 

Having thus described the invention there is claimed as new and desired to be secured by Letters Patent:
 1. A positioning system for cutaneously locating a target nerve or nerve plexus of a subject, the system comprising a carrier, a bore extending through the carrier, the bore having a proximal end and a distal end, the carrier having a surface with a smooth contour at the distal end of the bore, the surface being electrically nonconductive, a needle carried in the bore, the needle having a tip, the needle tip being selectively coupled to a current supply for eliciting a neurological response to current flow, the needle tip being in an operative cutaneous electrode position whereby current flow from the tip through the subject is assured when the surface is pressed against dermal layers of the subject without invasive penetration of the tip.
 2. A positioning system as constructed in accordance with claim 1 wherein a portion of the carrier is in engagement with the needle to releasably maintain the needle tip in the operative cutaneous electrode position.
 3. A positioning system as constructed in accordance with claim 2 wherein the needle includes a groove which is engaged by a portion of the carrier to releasably maintain the needle tip in the operative cutaneous electrode position.
 4. A positioning system as constructed in accordance with claim 2 wherein the needle includes a hub and a shaft, the shaft being engaged by a portion of the carrier to releasably maintain the needle tip in the operative cutaneous electrode position.
 5. A positioning system as constructed in accordance with claim 2 wherein the needle includes a hub and a shaft, the hub being engaged by a portion of the carrier to releasably maintain the needle tip in the operative cutaneous electrode position.
 6. A positioning system as constructed in accordance with claim 2 wherein the portion of the carrier in engagement with the needle comprises a set screw.
 7. A positioning system as constructed in accordance with claim 2 wherein the portion of the carrier in engagement with the needle comprises a pin.
 8. A positioning system as constructed in accordance with claim 1 wherein the carrier includes an axial slot extending from the bore and the needle includes a radial arm, the slot including at least one notch formed along a longitudinal edge thereof, the notch being dimensioned to receive the radial arm to releasably maintain the needle tip in the operative cutaneous electrode position.
 9. A positioning system as constructed in accordance with claim 1 wherein the bore comprises a first bore, the carrier having a second bore, the first bore and the second bore being coaxial, the second bore extending from the proximal end of the first bore, the needle including a proximal end and a distal end, the tip being positioned at the distal end of the needle and a hub being positioned at the proximal end of the needle, the second bore being dimensioned to receive the hub.
 10. A positioning system as constructed in accordance with claim 1 wherein the carrier includes an axial slot extending from the bore and the needle includes a radial arm received in the slot, whereby the radial arm may be employed for advancing the needle into the subject after the target nerve or nerve plexus has been located.
 11. A positioning system for locating a target nerve or nerve plexus of a subject, the system comprising a carrier, a bore extending through the carrier, the bore having a proximal end and a distal end, the carrier having a surface with a smooth contour at the distal end of the bore, the surface being electrically nonconductive, a needle carried in the bore, the needle having a tip, the tip being selectively coupled to a current supply, the tip having an operative position in proximity to the surface sufficient to assure current flow through the subject for eliciting a neurologic response which varies as a function of the position of the surface relative to the target nerve or nerve plexus.
 12. A method of locating a target nerve or nerve plexus of a patient for the administration of an anesthetic blockade or other medical procedure, the method comprising the steps of: a) providing a carrier having a bore and an electrically nonconductive smooth surface at an end of the bore, b) placing a needle having a tip within the bore, c) positioning the tip in proximity to the end of the bore, d) coupling a current supply to the tip, e) initiating current flow through the patient from the tip, f) moving the end of the bore while maintaining current flow; g) ascertaining a position of the carrier in registration with the target nerve or nerve plexus by eliciting a neurological response to current flow during step f) and h) fixing the carrier at the ascertained position.
 13. A method of administering an anesthetic blockade in accordance with claim 12 including the further steps of: i) advancing the tip beyond the end of the bore and toward the target nerve or nerve plexus, and j) detecting when the tip is properly positioned by observing when the maximal neural response is attained at the minimum current level.
 14. A method of locating a target nerve or nerve plexus for the administration of an anesthetic blockade or other medical procedure in accordance with claim 12 wherein the step of f) is practiced while applying a compressive force against dermal layers of the patient.
 15. A method of administering an anesthetic blockade in accordance with claim 14 including the further steps of: i) advancing the tip beyond the end of the bore and toward the target nerve or nerve plexus, and j) detecting when the tip is properly positioned by observing when the maximal neural response is attained at the minimum current level.
 16. A method of administering an anesthetic blockade in accordance with claim 12 including the further steps of: i) removing the carrier from the ascertained position, and j) advancing a needle into the patient at the ascertained position.
 17. A positioning system for locating a target nerve or nerve plexus of a subject constructed in accordance with claim 11 wherein the carrier includes a subcutaneous portion and a grip portion, the portions being cylindrical in shape and separated by a radial step, the bore extending through both portions, the grip portion having a larger diameter than the subcutaneous portion and the subcutaneous portion including the distal end of the bore.
 18. A method of administering an anesthetic blockade or other medical procedure to a patient, the method comprising the steps of: a) providing a needle having a tip, b) coupling a current supply to the tip, c) initiating current flow through the patient from the tip by noninvasively contacting dermal layers of the patient with the tip, d) varying the point of contact between the tip and the dermal layers, e) ascertaining a point of contact in registration with a target nerve or nerve plexus by eliciting a neurological response to current flow during step d) and f) advancing the needle into the patient at the ascertained point of contact.
 19. A method of administering an anesthetic blockade or other medical procedure to a patient in accordance with claim 18 wherein step d) is practiced in the absence of a coupling gel.
 20. A method of administering an anesthetic blockade in accordance with claim 12 wherein step f) is practiced in the absence of a coupling gel. 